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Renal hypoplasia is a developmental anomaly in which one or both kidneys (unilateral or bilateral renal hypoplasia, respectively (see these terms)) have a deficit in the number of nephrons and may be small. Oligomeganephronia (see this term) represents a severe variant of hypoplasia in which nephron number is reduced by 80% and nephrons are markedly hypertrophied.
ORPHA:93101Classification level: Disorder
- Synonym(s): -
- Prevalence: Unknown
- Inheritance: Not applicable or Autosomal dominant
- Age of onset: All ages
- ICD-10: Q60.3 Q60.4 Q60.5
- OMIM: -
- UMLS: C0266295 C2608080
- MeSH: -
- GARD: -
- MedDRA: 10049102
Pure renal hypoplasia is considered rare and, given the difficulty to distinguish it from renal dysplasia (see this term) that also results in small kidneys, its prevalence and incidence are unknown.
Renal hypoplasia is usually asymptomatic, but a small kidney can be detected with a routine ultrasound screening performed during pregnancy, after a urinary tract infection in children, or during renal disease in adults. Disease severity depends on the degree of reduction in the number of nephrons, and on the involvement of one or both kidneys. The disease may lead to glomerular hyperfiltration associated with hypertension, proteinuria and, in the long run, with chronic renal failure. When not diagnosed early, its presentation may include consequences of renal insufficiency, such as anemia or growth stunting. Such clinical consequences are not easily delineated, but renal dysplasia and renal hypoplasia account for 35-50% of the causes of chronic kidney disease in children.
The occurrence of renal hypoplasia has been linked to several factors such as intrauterine growth restriction, maternal diseases (diabetes, hypertension), maternal drug intake (inhibitors of the renin-angiotensin system or non-steroidal anti-inflammatory drugs (NSAIDs)) and intoxication (smoking and alcohol). Premature birth (before the 36th week) is also a risk factor due to incomplete nephrogenesis. Renal hypoplasia can be part of a multi-organ syndrome such as renal coloboma syndrome (due to mutations in the PAX2 gene (10q24.31)), Turner syndrome (see these terms) or 22q11 deletion syndrome. An influence of common variants in the PAX2, RET (10q11.2), ALDH1A2 (15q21.2), and OSR1 (2p24.1) genes have been described.
Diagnosis is suggested by ultrasonography. On fetal or postnatal ultrasound, renal hypoplasia is defined as a kidney mass of below two standard deviations of that of an age-matched normal individual or a combined kidney mass of less than half of normal for the patient's age. However, it should be noted that adult renal size is not a proper marker of nephron numbers, and that most cases of small kidneys are caused by renal dysplasia. As the distinction can only be made by histology, which is not performed in routine clinical care, diagnosis is generally not confirmed definitively. Postnatal renography with technetium-99m-labeled dimercaptosuccinic acid shows smooth kidney outline.
Histological features can distinguish renal hypoplasia from various forms of renal dysplasia. Small kidneys in children may also be due to scarring after pyelonephritis, neonatal renal vein thrombosis or severe renal artery stenosis.
Antenatal ultrasonographic screening is becoming routine and allows detection of renal hypoplasia from midway through gestation.
Most cases are sporadic. Familial cases have been observed with an autosomal dominant transmission and thus a recurrence risk of 50% in such cases.
Management and treatment
Management largely depends on the reduction in number of nephrons, which is very difficult to predict. Therefore, assessment of renal function (blood pressure, estimate of the glomerular filtration rate and proteinuria) should be obtained to evaluate the function of the remaining nephrons. Due to an increased risk of hypertension and/or proteinuria, individuals with renal hypoplasia deserve long-term follow-up. In extreme cases, renal replacement therapy may be needed.
The risk of renal failure in childhood is minimal but may occur in severe cases.